Showing papers in "Optics Letters in 1996"
TL;DR: The fabrication of a new type of optical waveguide: the photonic crystal fiber that supports a single robust low-loss guided mode over a very broad spectral range of at least 458-1550 nm.
Abstract: We report the fabrication of a new type of optical waveguide: the photonic crystal fiber. It consists of a pure silica core surrounded by a silica-air photonic crystal material with a hexagonal symmetry. The fiber supports a single robust low-loss guided mode over a very broad spectral range of at least 458-1550 nm. Also see errata - http://eprints.soton.ac.uk/78010/
2,991 citations
TL;DR: The results suggest that multiphoton interactions occur in the glasses and that it may be possible to write three-dimensional optical circuits in bulk glasses with such a focused laser beam technique.
Abstract: With the goal of being able to create optical devices for the telecommunications industry, we investigated the effects of 810-nm, femtosecond laser radiation on various glasses. By focusing the laser beam through a microscope objective, we successfully wrote transparent, but visible, round-elliptical damage lines inside high-silica, borate, soda lime silicate, and fluorozirconate (ZBLAN) bulk glasses. Microellipsometer measurements of the damaged region in the pure and Ge-doped silica glasses showed a 0.01–0.035 refractive-index increase, depending on the radiation dose. The formation of several defects, including Si E′ or Ge E′ centers, nonbridging oxygen hole centers, and peroxy radicals, was also detected. These results suggest that multiphoton interactions occur in the glasses and that it may be possible to write three-dimensional optical circuits in bulk glasses with such a focused laser beam technique.
2,500 citations
TL;DR: A novel class of highly sensitive sensors based on long-period fiber gratings that can be implemented with simple and inexpensive demodulation schemes are presented.
Abstract: We present a novel class of highly sensitive sensors based on long-period fiber gratings that can be implemented with simple and inexpensive demodulation schemes. Temperature, strain, and refractive-index resolutions of 0.65 °C, 65.75 μ∈, and 7.69 × 10−5, respectively, are demonstrated for gratings fabricated in standard telecommunication fibers.
1,267 citations
TL;DR: It is demonstrated that quality factor Q - (0.8 +/- 0.1) x 10(10) of whispering-gallery modes in fused-silica microspheres at 633 nm, close to the ultimate level determined by fundamental material attenuation as measured in optical fibers, is demonstrated.
Abstract: We demonstrate the quality factor Q - (0.8 +/- 0.1) x 10(10) of whispering-gallery modes in fused-silica microspheres at 633 nm, close to the ultimate level determined by fundamental material attenuation as measured in optical fibers. The lifetime of ultimate Q is limited by adsorption of atmospheric water. Monitoring of adsorption kinetics with submonolayer sensitivity by Q factors and frequencies of whispering-gallery modes is demonstrated. The possibility of supermaterial Q's owing to intrinsic suppression of scattering losses in micropheres is discussed.
986 citations
TL;DR: A cross-phase modulation scheme that exhibits a giant, resonantly enhanced nonlinearity, along with vanishing linear susceptibilities, is analyzed and has possible applications in quantum nondemolition measurements and for quantum logic gates.
Abstract: We analyze a cross-phase modulation (XPM) scheme that exhibits a giant, resonantly enhanced nonlinearity, along with vanishing linear susceptibilities The proposed atomic system uses an electromagnetically induced transparency and is limited only by two-photon absorption We predict dramatic improvement by several orders of magnitude for conditional phase shifts in XPM, and the system has possible applications in quantum nondemolition measurements and for quantum logic gates
972 citations
TL;DR: A novel method for three-dimensional optical data storage that has submicrometer size resolution, provides a large contrast in index of refraction, and is applicable to a wide range of transparent materials is presented.
Abstract: We present a novel method for three-dimensional optical data storage that has submicrometer size resolution, provides a large contrast in index of refraction, and is applicable to a wide range of transparent materials. Bits are recorded by use of a 0.65-N.A. objective to focus 100-fs laser pulses inside the material. The laser pulse produces a submicrometer-diameter structurally altered region with high contrast in index of refraction. We record binary information by writing such bits in multiple planes and read it out with a microscope objective with a short depth of field. We demonstrate data storage and retrieval with 2-microm in-plane bit spacing and 15-microm interplane spacing (17 Gbits/cm(3)). Scanning electron microscopy and atomic force microscopy show structural changes confined to an area 200 nm in diameter.
959 citations
TL;DR: It is shown that one can in principle generate fields of any integral order P by cascading such elements and devices that generate P = 1 fields are achromatic and can be used as polarization axis finders or as versatile tools for studying birefringent or polarizing materials.
Abstract: Novel liquid-crystal devices are described that generate linearly polarized light with axial symmetry; the beam propagation axis is the symmetry axis. Such light fields can be characterized by a polarization order number P. For example, P = 1 fields represent radially or azimuthally polarized light. The reorientation of the polarization orientation in these polarization converters is due to the twisted nematic effect and the effect of lambda/2 wave plates. A single polarization converter can generate fields of orders 1 and 2. It is shown that one can in principle generate fields of any integral order P by cascading such elements. Devices that generate P = 1 fields are achromatic and can be used as polarization axis finders or as versatile tools for studying birefringent or polarizing materials.
573 citations
TL;DR: Long-period fiber gratings are used to f latten the gain spectrum of erbium-doped fiber amplifiers and it is shown that a chain of amplifiers can be equalized, leading to a bandwidth enhancement by a factor of 3.
Abstract: Long-period fiber gratings are used to flatten the gain spectrum of erbium-doped fiber amplifiers. A broadband amplifier with <0.2-dB gain variation over 30 nm is presented. We also show that a chain of amplifiers can be equalized, leading to a bandwidth enhancement by a factor of 3.
500 citations
TL;DR: A novel configuration of a distributed fiber sensor by Brillouin gain analysis using a single laser source, and the required light signals are all generated with an electro-optic modulator, resulting in high stability and excellent reliability of the measuring setup.
Abstract: A novel configuration of a distributed fiber sensor by Brillouin gain analysis has been developed for temperature and strain monitoring. It uses a single laser source, and the required light signals are all generated with an electro-optic modulator, resulting in high stability and excellent reliability of the measuring setup. Measurement of the induced strain in a wound fiber is presented as a demonstration of the system performance.
472 citations
TL;DR: The conical emission is attributed to Cerenkov radiation from a dynamic self-guiding structure consisting of a weakly ionized core surrounded by Kerr cladding.
Abstract: Conical emission in the forward direction is observed from intense femtosecond light pulses propagating through air over long distances. The conical emission is attributed to Cerenkov radiation from a dynamic self-guiding structure consisting of a weakly ionized core surrounded by Kerr cladding.
417 citations
TL;DR: A new scheme that shows large angular dispersion is proposed and demonstrated, and low polarization-state dependence (~0.1 dB) is also confirmed.
Abstract: A new scheme that shows large angular dispersion is proposed and demonstrated. The key idea to this method is a virtually imaged phased array (VIPA). The angular dispersion of a VIPA is 10–20 times larger than those of common diffraction gratings, which have blaze angles of ~30 deg. With the VIPA, wavelength demultiplexing for 10 channels with 0.8-nm spacing is achieved. Low polarization-state dependence (~0.1 dB) is also confirmed.
TL;DR: An experimental apparatus capable of exploring the phase sensitivity of nonlinear-optical interactions is presented and a feasibility study of controlling the carrier phase in ultrashort light-wave packets emitted by a sub-10-fs laser is reported.
Abstract: A feasibility study of controlling the carrier phase in ultrashort light-wave packets emitted by a sub-10-fs laser is reported. An experimental apparatus capable of exploring the phase sensitivity of nonlinear-optical interactions is presented.
TL;DR: Phase-contrast microscopy shows that the structure of the refractive-index inhomogeneities in a variety of mammalian tissues resembles that of frozen turbulence, and the observed structure function fits the classical Kolmogorov model of turbulence.
Abstract: Phase-contrast microscopy shows that the structure of the refractive-index inhomogeneities in a variety of mammalian tissues resembles that of frozen turbulence. Viewed over a range of scales, the spectrum of index variations exhibits a power-law behavior for spatial frequencies spanning at least a decade (0.5–5 μm−1) and has an outer scale in the range of 4–10 μm, above which correlations are no longer seen. The observed structure function fits the classical Kolmogorov model of turbulence. These observations are fundamental to understanding light propagation in tissue and may provide clues about how tissues develop and organize.
TL;DR: Gain of 10-18 dB is obtained as the signal wavelength was tuned over a 35-nm bandwidth near 1560 nm and the amplifier was operated near the fiber's zero-dispersion wavelength.
Abstract: The bandwidth of a single-pump fiber optical parametric amplifier is governed by the even orders of fiber dispersion at the pump wavelength. The amplifier can exhibit gain over a wide wavelength range when operated near the fiber's zero-dispersion wavelength. It can also be used for broadband wavelength conversion,with gain. We have experimentally obtained gain of 10-18 dB as the signal wavelength was tuned over a 35-nm bandwidth near 1560 nm.
TL;DR: Dynamic, motion-artifact-free in vivo imaging of a beating Xenopus laevis (African frog) heart is demonstrated.
Abstract: The development of techniques for high-speed image acquisition in optical coherence tomography (OCT) systems is essential for suppressing motion artifacts when one is imaging living systems. We describe a new OCT system for performing micrometer-scale, cross-sectional optical imaging at four images/s. To achieve OCT image-acquisition times of less than 1 s, we use a piezoelectric fiber stretcher to vary the reference arm delay. A Kerr-lens mode-locked chromium-doped forsterite laser is employed as the low-coherence source for the highspeed OCT system. Dynamic, motion-artifact-free in vivo imaging of a beating Xenopus laevis (African frog) heart is demonstrated.
TL;DR: M/# is introduced as a metric for characterizing holographic memory systems and it is verified experimentally that the diffraction efficiency of multiple holograms follows the prediction of M/# measured from a single hologram.
Abstract: We introduce M/# as a metric for characterizing holographic memory systems. M/# is the constant of proportionality between diffraction efficiency and the number of holograms squared. Although M/# is a function of many variables in a holographic recording system, it can be measured from the recording and erasure of a single hologram. We verify experimentally that the diffraction efficiency of multiple holograms follows the prediction of M/# measured from a single hologram.
TL;DR: The inverse problem for f luorescence lifetime tomography is formulated using diffuse photon density waves, and the technique is demonstrated by deriving spatial images of heterogeneous f l luorophore distribution and lifetime, using simulated measurements in heterogeneous turbid media.
Abstract: The lifetime of a fluorophore generally varies in different environments, making the molecule a sensitive indicator of tissue oxygenation, pH, and glucose. However, lifetime measurements are complicated when the fluorophore is embedded in an optically thick, highly scattering medium such as human tissue. We formulate the inverse problem for fluorescence lifetime tomography using diffuse photon density waves, and we demonstrate the technique by deriving spatial images of heterogeneous fluorophore distribution and lifetime, using simulated measurements in heterogeneous turbid media.
TL;DR: A theory of optical pulse propagation in cascaded transmission systems that are based on the dispersioncompensatingfiber technique is developed and the existence of two scales associated with fiber dispersion and system residual dispersion leads to a simple model for the averaged pulse dynamics.
Abstract: A theory of optical pulse propagation in cascaded transmission systems that are based on the dispersion-compensating fiber technique is developed. The existence of two scales associated with fiber dispersion and system residual dispersion leads to a simple model for the averaged pulse dynamics. In the particular case of practical importance, the averaged pulse dynamics is governed by the nonlinear Schrodinger equation. The pulse transmission stability is examined.
TL;DR: Experiments in which Mie-scattering particles were optically driven in the evanescent field that is generated in a channeled waveguide found polystyrene latex spheres with diameters of 1-5 microm laterally trapped and longitudinally driven along the direction of the waveguide channel.
Abstract: We report a series of experiments in which Mie-scattering particles were optically driven in the evanescent field that is generated in a channeled waveguide. Polystyrene latex spheres with diameters of 1-5 microm were laterally trapped within the evanescent field, which was produced by a cw laser beam incident upon the waveguide and then longitudinally driven along the direction of the waveguide channel at speeds of as much as 14 microm/s. Metallic spheres of gold (0.5-microm diameter) and platinum (1-microm diameter) were also laterally trapped and longitudinally moved along the waveguide channel.
TL;DR: In this article, a method for measuring the nonlinear refractive index of optical fibers with an error of less than 5% is demonstrated, based on measuring the phase shift experienced by a dual-frequency beat signal, permitting a simple, highly sensitive, accurate, repeatable, and easily automated measurement procedure and sampling.
Abstract: A method for measuring the nonlinear refractive index of optical fibers with an error of less than 5% is demonstrated. The technique is based on measuring the nonlinear phase shift experienced by a dual-frequency beat signal, permitting a simple, highly sensitive, accurate, repeatable, and easily automated measurement procedure and sampling. Measurements of the nonlinear coefficient in standard telecommunication, dispersion-shifted, and a number of dispersion-compensated fibers are presented.
TL;DR: It is demonstrated theoretically and experimentally that optical beams are self-focused and self-trapped upon initiating photopolymerization and the resulting nonlinear wave equation is shown to be nonlocal in time and displays self-Trapped solutions only for sufficiently low average optical intensities.
Abstract: We demonstrate theoretically and experimentally that optical beams are self-focused and self-trapped upon initiating photopolymerization. This unique nonlinear optical phenomenon is dependent on the optical exposure and produces permanent index-of-refraction changes larger than 0.04. The resulting nonlinear wave equation is shown to be nonlocal in time and displays self-trapped solutions only for sufficiently low average optical intensities.
TL;DR: Two cw, singly resonant optical parametric oscillator (OPO) configurations based on periodically poled lithium niobate that result in significantly higher efficiency and output power than in previous studies are reported.
Abstract: We report two cw, singly resonant optical parametric oscillator (OPO) configurations based on periodically poled lithium niobate that result in significantly higher efficiency and output power than in previous studies. Using four-mirror OPO cavities and pumping with a 1.064-microm Nd:YAG laser, we observe 93% pump depletion and obtain ~86% of the converted pump photons as useful idler output. The single-beam, in-the-bucket idler output power of 3.55 W at 3.25 microm corresponds to ~80% of quantum-limited performance. We measure and compare the amplitude noise and spectral bandwidth of the two configurations. We also demonstrate >1 W of tunable cw output over the 3.3-3.9-microm spectral range.
TL;DR: The extraordinary polarization of LiNbO(3) has better IR transmission than does the ordinary polarization, permitting operation at longer wavelengths with d(33) quasi-phase matching than with conventional Type I birefringent phase matching.
Abstract: We report a widely tunable quasi-phase-matched optical parametric oscillator that uses periodically poled LiNbO3 with a multigrating structure. The device is tuned by translation of the crystal through the resonator and pump beam, with no realignment needed. With a 1.064-μm acousto-optically Q-switched Nd:YAG pump laser, we produced noncritically phase-matched tunable IR output from 1.36 to 4.83 μm. The threshold was 6 μJ for a 26-mm interaction length. The extraordinary polarization of LiNbO3 has better IR transmission than does the ordinary polarization, permitting operation at longer wavelengths with d33 quasi-phase matching than with conventional Type I birefringent phase matching.
TL;DR: In this article, an all-solidstate Kerr-lens mode-locked Cr:forsterite laser operating at 1.28 μm is demonstrated as a shortcoherence-length, high-average-power source for optical coherence tomographic (OCT) imaging.
Abstract: An all-solid-state Kerr-lens mode-locked Cr:forsterite laser operating at 1.28 μm is demonstrated as a shortcoherence-length, high-average-power source for optical coherence tomographic (OCT) imaging. We achieve ultrahigh resolution by spectrally broadening the laser pulses, using self-phase modulation in a dispersion-shifted single-mode fiber. OCT imaging with a resolution of 6 μm and a dynamic range of 115 dB is achieved.
TL;DR: Efficient, electrically tunable, agile, inertialess, near-diffraction-limited one-dimensional optical beam steering is demonstrated at the infrared wavelength of 10.6 microm with a liquid-crystal phased array.
Abstract: Efficient, electrically tunable, agile, inertialess, near-diffraction-limited one-dimensional optical beam steering is demonstrated at the infrared wavelength of 10.6 microm with a liquid-crystal phased array.
TL;DR: Two recently reported solutions are members of a family of localized Bessel-Gauss beam solutions that can describe the entire transverse electric field in the paraxial limit.
Abstract: The Hermite–Gauss and Laguerre–Gauss modes are well-known beam solutions of the scalar Helmholtz equation in the paraxial limit. As such, they describe linearly polarized fields or single Cartesian components of vector fields. The vector wave equation admits, in the paraxial limit, of a family of localized Bessel–Gauss beam solutions that can describe the entire transverse electric field. Two recently reported solutions are members of this family of vector Bessel–Gauss beam modes.
TL;DR: It is shown that frequency-resolved optical gating combined with spectral interferometry yields an extremely sensitive and general method for temporal characterization of nearly arbitrarily weak ultrashort pulses even when the reference pulses is not transform limited.
Abstract: We show that frequency-resolved optical gating combined with spectral interferometry yields an extremely sensitive and general method for temporal characterization of nearly arbitrarily weak ultrashort pulses even when the reference pulses is not transform limited. We experimentally demonstrate measurement of the full time-dependent intensity and phase of a train of pulses with an average energy of 42 zeptojoules (42 × 10−21 J), or less than one photon per pulse.
TL;DR: A miniature confocal optical microscope for monochromatic imaging that uses single-mode fiber illumination and a two-phase off-axis zone plate objective lens and has 1.0-microm resolution over a 100- microm field of view is constructed.
Abstract: We have constructed a miniature confocal optical microscope for monochromatic imaging that uses single-mode fiber illumination and a two-phase off-axis zone plate objective lens. The scanning mechanism consists of two micromachined silicon torsional scanning mirrors with orthogonal axes of rotation. The objective lens is made of fused silica and has a N.A. of 0.24 at lambda = 0.6328 microm, with a 1.0-mm working distance. The device is side looking, with die dimensions of 1.2 mm x 2.5 mm x 6.5 mm. We have measured 1.0-microm resolution over a 100-microm field of view.
TL;DR: An algorithm in which the desired shape is obtained in the fractional Fourier or the Fresnel domain is proposed, which can reduce the error between the theoretically desired shape and the actual output by 30 times over the conventional G-S algorithm.
Abstract: The Gerchberg–Saxton (G–S) algorithm is a well-known procedure used in various optical implementations. One of its most common applications is beam shaping of an input plane. In that application the desired beam shape is obtained in the Fourier plane. We propose an algorithm in which the desired shape is obtained in the fractional Fourier or the Fresnel domain. Computer simulations illustrate that the newly defined algorithm can reduce the error between the theoretically desired shape and the actual output by 30 times over the conventional G–S algorithm.
TL;DR: A new sensing technique for the distributed measurement of temperature and strain, based on Brillouin optical frequency-domain analysis, is presented and the first experimental results demonstrate the feasibility of this new concept.
Abstract: A new sensing technique for the distributed measurement of temperature and strain, based on Brillouin optical frequency-domain analysis, is presented. Theoretical investigations and first experimental results of distributed measurements demonstrate the feasibility of this new concept.